Electron discharge device



Oct. 22, 1940. E w HEROLD I ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed April 28, 193'! INVENTOR EDWARD IV HEIQOLD ATTORN EY Oct. 22, 1940.

E. w. HEROLD ELECTRON DISCHARGE DEVICE Filed April 28, 1937 2 Sheets-Sheet 2 INVENTOR EDWARD m HEROLD flf/Zur ATTORNEY Patented Oct. 22, 1940 UNITED STATES PATENT OFFlCE ELECTRON DISCHARGE DEVICE Delaware Application April 28, 1937, Serial No. 139,375

10 Claims.

My invention relates to electron discharge devices for superheterodyne reception, and more particularly to a multi-electrode electron discharge device in which local oscillations of predetermined frequency and input oscillations of a different frequency, such as a radio signal, are mixed or combined within the device.

In radio receivers employing the superheterodyne method of reception alternating voltages of two different frequencies must be combined; that is, the signal voltage of one frequency received by the antenna and usually amplified in the preceding stage must be combined with the local oscillator voltage at a different frequency produced by the local oscillator in the receiver proper so that a heterodyne action will produce an alternating voltage of an intermediate frequency modulated in the same manner as the signal voltage.

Usual methods of a heterodyne reception employ a first detector or mixer tube in which the radio signal (input frequency) and the local oscillations of a different frequency generated in an oscillator circuit usually by a separate tube are both applied to the same tube but on different grids. This mixing action in modern receivers may be accomplished by means of two different types of tubes, one the so-called pentagrid converter, which has several grids, the oscillator grid being the inner grid near the cathode and the signal grid being an outer grid. This tube performs both the functions of the oscillator and mixer. The converter type of tube in which both functions are performed meets with several difliculties, the two major ones being space charge coupling between the oscillator and signal sections, and the change of oscillator frequency when automatic volume control voltage is applied to the tube. These difliculties were overcome to a. certain extent by placing the signal voltage on an inner grid and the oscillator voltage on an outer grid. This method of operation, however, prevented a tube design which could combine the functions of an oscillator and mixer in the same section of the tube due principally to the fact that the oscillator would cease functioning when the signal or control grid became sufliciently negative to cut off the electron stream to the oscillator portion of the tube. For high frequencies, therefore, it was found more desirable to use the so-called straight mixer tube having a signal grid and an oscillator grid to which the oscillator voltage is applied by a separate tube or a separate group of electrodes in the same envelope effective as a separate tube to provide the oscillator voltage.

When the higher frequencies were encountered,

however, it was found that even the mixer tube was subject to certain objections because of the transit time effect in the tubes which caused grid current to flow in the first or signal grid when the second or oscillator grid voltage was high in fre- 5 quency, This effect is explained as due to the electrons which are periodically repelled by the oscillator grid when it goes negative; that is, electrons which are in the space between the signal grid and the oscillator grid when the oscillator grid 10 swings negative are returned to the signal grid. It was also discovered that the signal grid input resistance was quite low at the high frequencies and most of this so-called transit time loading was also due to the electrons repelled by the os- 1 cillator grid to the vicinity of the first grid.

It is the principal object of my invention to provide an improved type of mixer tube for use in superheterodyne receivers, more particularly to provide sucha tube in which the transit time 20 effects described above are substantially eliminated.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the inven- 25 tion itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 isa transverse cross section of the mount of an electron discharge device illustrating and em- 30 bodying the principles of my invention; Figure 2 is a practical form of an electron discharge device made according to my invention; Figure 3 is a perspective view partially in section to show details of construction of an electron discharge de- 85 vice which has been found most satisfactory; Figure 4 is a cross section taken along the line 44 of Figure 3; Figure 5 is a cross section of the mount of a still further modification of an electron discharge device made according to my in- 40 vention; and Figure 6 is a conventional circuit in which an electron discharge device made according to my invention is incorporated.

In the conventional mixer tube such as shown in the Llewellyn Patent 1,876,780, issued February 45 7, 1933, and assigned to the Bell Telephone Laboratories, the cathode is surrounded in turn by a signal grid, a screen grid, an oscillator grid to which the local oscillation is applied, and a second screen grid, and an anode. quencies the time required for the electrons to travel from the cathode to the anode is long enough so that electrons may be caught in flight between the signal grid and the oscillator grid when the oscillator grid goes negative. These 55 At very high fre- V electrons are sometimu repelled by the negative oscillator grid and return to the signal grid with an appreciably increased velocity. By means of my invention the electrons which are repelled by the oscillator grid are swept out of the space between the signal grid and oscillator grid and prevented i'rom returning to the signal grid.

A better understanding of the action may be obtained by referring to Figure 1 showing a cross section of a mount of a tube embodying the principles upon which my invention is based. A cathode III is surrounded in turn by a signal grid ll, screen grid l2, oscillator grid I3, screen grid l4 and anode II. A suppressor grid l6 can be added if desired. Each of the grids is provided with oppositely disposed side rods, the side rods lying in a common plane, With the construction so far described, which is the conventional mixer tube, the electrons are projected in two more or less well defined streams or beams from opposite sides of the cathode due to the action of the signal grid side rods. In normal operation when the oscillator grid I3 is swung negative by the applied oscillator voltage, the electrons are prevented from reaching the anode I 5 and are returned to the region of the signal grid through the screen grid l2 which is at a high positive potential. The eiIect of the returned electrons is to cause the signal grid to exhibit a very low input resistance at high frequencies. In addition, some of the electrons have appreciably increased velocities because of the change in oscillator grid potential during the time the electrons are in the region between grids l2 and I2. The increased velocity is sometimes suflicient to permit electrons to strike the negatively biased signal grid l I.

In accordance with my invention I place between the signal grid and oscillator grid, and in line with the siderods, a pair of auxiliary electrodes II, which are maintained at a high positive potential with respect to the signal grid and the oscillator grid and being preferably at a higher potential than the screen grid l2. The result of this applied voltage is to cause the stream of electrons on either side to travel in more or less curved paths as indicated by the dotted lines from the cathode to the anode. It will thus be seen that most of the electrons are made to pass considerably closer to the side rods than when the eelctrodes I! are not present. Electrons caught between the signal grid and the oscillator grid under these conditions will not return to the region of the signal grid but will be returned as indicated by the dotted lines to the auxiliary electrodes ll, which are at the higher positive potential. These returning electrons are indicated for only one-half of the tube, it being understood that this action takes place on both sides. In this way the electrons which would normally be returned by the oscillator grid going negative are swept from the-field between the signal and oscillator grids and are rendered ineiIective to cause grid current and low signal resistance;

In Figure 2 a modified'form of tube is shown which is an improvement over that shown in Figure 1. The form shown in Figure 2 eliminates the necessity for separate auxiliary electrodes and the necessary leads andresults in a simpler construction in which the high potential small auxiliary anodes are replaced by lower potential but much larger auxiliary anodes. In this arrangement the cathode is surrounded by a control grid 2| and screen grid 22, followed in turn by the oscillator grid 23, screen grid 24, suppreuorfl andanode 2|. Inthisform theauxil iary electrodes 21 and 28 have the form of channel members attached on'the outside oi. the screen grid to the screen grid side rods so that oppositelydisposed slots are provided for the electrons issuing from the cathode. This construction also has the advantages characteristic of the form shown in Figure 1, but is in addition simpler in construction.

The preferred embodiment ,of my invention.

disclosed in Figure 3 and embodied in a tube of the metal envelope type includes a metal envelope II in which themount assembly is contained. The mount is positioned between a pair of shielding members Ii and 22 supporting the mica insulating spacers 33 and 34 which insulatingly support and space the electrodes from each other. As best shown in Figure 4, the oathode comprises a tubular member 35 of rectangular cross section. The flat opposite sides only preferably are coated, which assists in the beam torn ration of the electrons from thecathode to the anode. The cathode in turn is surrounded by a control grid 36, the wires of which are parallel to the flat coated surfaces of thecathode,

the side rods 36' being opposite the non-coatedsurfaces of the cathode, a screen grid 31, oscillator grid 38, screen 39, suppressor 40 and anode 4|. The collecting electrodes or auxiliary electrodes 42 are in the form of channel members electrically connected to the screen grid side rods and oppositely disposed to provide a pair of oppositely disposed slots or apertures through which the beams of electrons from the cathode are directed toward the anode. This form of tube made according to my invention is an improvement over that shown in Figures 1 and 2.

A still further modification of my invention is shown in Figure 5 wherein the oscillator grid 44 is provided with a pair of oppositely disposed side rods 45 positioned in the electron beams and open spaces or slots between the auxiliary collector electrodes 42. These rods assist in causing the prlmaryelectrons from the cathode to.

travel a curved path and further insure that electrons returned by the oscillator grid are returned to the solid shield auxiliary electrodes on the screen grid. Only a part of the electron stream is shown by slotted lines to indicate the paths oi electrons which reach the plate and those that are returned to the collecting electrodes or shields 42. This still further improves the operation 'of the tube shown in Figures 1 and 2.

The application of a tube made according to my invention to a conventional circuit is shown in Figure 6 in which the tuned circuit comprising the inductance and variable capacity 5| is connected between cathode 35 and control grid 36. The screen grids 3'! and 39 are connected to the usual source of voltage, the oscillator grid 38 being connected to a separate local oscfllator 52. The output from the anode is fed through the primary of the coupling transformer 53.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or theme indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departin the appended claims.

What I claim as new is:

1. An electron discharge device having a thermionic cathode for supplying a stream of electrons, an anode for receiving said stream of electrons, a first control electrode adjacent said cathode for controlling the movement of the electrons in said stream from said cathode to said anode, a second control electrode between said first control electrode and said anode and adapted to have a varying negative and positive potential of high frequencies applied thereto, and means positioned outside of and to one side of said stream of electrons and between said first and second control electrodes for receiving electrons returned by said second control electrode when said second control electrode assumes a negative potential with respect to said cathode during operation of said electron discharge device.

2. An electron discharge device having a thermionic cathode for supplying a stream of electrons and an anode for receiving said stream of electrons, a first control electrode, a screen electrode and a second control electrode in succession in position between said cathode and anode, said second control electrode being adapted to have a varying positive and negative potential of high frequency applied thereto, and means between the screen electrode and said second control electrode and positioned outside of and to one side of said stream of electrons for receiving electrons returned by said second control electrode, when said second control electrode becomes negatively charged during operation of said electron discharge device.

3. An electron discharge device having a cathode and a control electrode adjacent thereto for providing a stream of electrons, an anode for receiving said stream of electrons, a second control electrode positioned in the stream of electrons between said first control electrode and said anode and adapted to have positive and negative potentials of high frequency applied thereto, and means positioned at the side of said stream of electrons for receiving electrons returned by said second control electrode when said second control electrode becomes negative.

4. An electron discharge device having a cathode for supplying electrons and surrounded by a first control grid, a screen grid, a second control grid and an anode, said first control grid being provided with oppositely disposed side rods whereby the electrons from said cathode move in two oppositely disposed beams between said side rods to said anode, said second control grid being adapted to have a varying negative and positive potential of high frequency applied thereto, and means on opposite sides of said beams between the two control grids for receiving electrons returned by said second control grid when a negative voltage is applied to said second control grid.

5. An electron discharge device having a cathode for supplying electrons surrounded by a first control grid, a screen grid, a second control grid and an anode for receiving said electrons, said cathode and grids adapted to cause the electrons from said cathode to move in beams to said anode, said second control electrode being adapted to have varying negative and positive potentials of high frequency applied thereto, and a pair of oppositely disposed channel members connected to said screen grid on opposite sides of said beams for receiving electrons returned by said second control grid when negative potentials are applied to said second control grid during operation of the electron discharge device.

6. An electron discharge device containing a cathode having a fiat surface coated with emitting material for supplying electrons, a control electrode adjacent said cathode and lying parallel to said fiat surface and provided with a pair of oppositely disposed members at opposite edges of the fiat cathode for providing a beamof electrons, an anode for receiving said beam of electrons, a second control electrode in the path of said beam of electrons adapted to have varying positive and negative potentials of high frequency applied thereto, and means on opposite sides of said beam for receiving electrons returned by said second control electrode when said control electrode becomes negative during operation of said electron discharge device.

7. An electron discharge device containing a cathode having a fiat surface coated with emitting material for supplying electrons, a control electrode adjacent said cathode and having grid wires parallel to said flat surface and provided with a pair of oppositely disposed members at opposite edges of the flat cathode for providing a beam of electrons, an anode for receiving said beam of electrons, a second control electrode in the path of said beam of electrons adapted to have varying positive and negative potentials at high frequency applied thereto, and means on opposite sides of said beam for receiving electrons returned by said second control electrode when said control electrode becomes negative during operation of said electron discharge device.

8. An electron discharge device containing a thermionic cathode having two opposite flat surfaces coated with eectron emitting material the surfaces between being uncoated, a control grid surrounding said cathode and having grid wires parallel to the flat emitting surfaces of said cathode and a pair of oppositely disposed side rods positioned adjacent the non-emitting surfaces of said cathode whereby a pair of oppositely directed beams of electrons is formed, and an anode for receiving said beams of electrons, a screen grid surrounding said control grid, a second control grid surrounding said screen grid and adapted to have varying negative and positive potentials of high frequency applied thereto, and a pair of oppositely disposed channel shaped members supported by and electrically connected to said screen grid and providing a pair of apertures in said screen grid through which the beams of electrons pass, said channel shaped members being adapted to receive electrons returned by said second control grid when a negative potential is applied thereto during the operation of said electron discharge device.

9. An electron discharge device containing a thermionic cathode having a rectangular shaped cross section, only two of the opposite fiat surfaces of said cathode being coated with electron emitting material, and a control grid surrounding said cathode and having grid Wires parallel to the fiat emitting surfaces of said cathode, and a pair of oppositely disposed side rods positioned adjacent the non-emitting surfaces of said cathode Whereby a pair of oppositely disposed electron beams is formed and an anode for receiving the electrons, a screen grid surrounding said control grid, a second control grid surrounding said screen grid, said second control electrode being adapted to have varying negative and positive high freoppositely disposed channel shaped members supported by and electrically connected to said screen grid and providing a pair of apertures in said screen grid through which the beams of electrons pass, said channel shaped members being adapted to receive electrons returned by said second control grid when a negative potential is applied thereto during the operation of said electron discharge device, said second control grid being provided with a pair of oppositely disposed side rods in the path of said beams, whereby said beams are divided and caused to flow in outwardly directed curved paths between the second control grid and said channel members.

10-. A thermionic device containing a thermionic cathode having oppositely disposed flat surfaces coated with an emitting material, a control grid surrounding said cathode and having grid wires parallel 'to said emitting surfaces, and oppositely disposed side rods adjacent the edges of said flat surfaces, a rectangularly shaped screen electrode positioned on the outside 0! said control grid, said control grid and cathode providing oppositely directed beams of electrons, and an anode for receiving said beams oi electrons, a second control grid surrounding said screen grid and provided with a, pair 01' oppositely disposed side rods positioned in the path of said electron beams whereby said beams are divided and caused to flow in curved paths away from said side rods, said second control electrode being adapted to have varying positive and negative voltages 01' high frequency applied thereto, and oppositely disposed channel shaped members supported by and electrically connected to said screen grid whereby a pair 01' oppositely disposed apertures are provided for said electron beams, said channel shaped members being adapted to receive said electrons returned by said second control electrode when said second control electrode has a negative potential applied thereto during operation 01' said electron discharge device.

EDWARD W. HEROLD. 

